The way it was explained to me was to think of the field as tapping into a 'pool' of crude, and with directional drilling, they can tap into it from the bottom to effectively drain that pool. The same principle would apply to oil rigs at sea. The person explaining that was explicitly denying abiotic oil as possible because of how they can drain the deposit.

If this theory is true (and I have little reason to doubt it, just not enough to prove it) then it's really just a matter of draining the reservoir faster than it would be replenished.

They would argue that it's because of better methods and instruments that, since the 'peak oil panic' (70's, IIRC), there are currently more proven oil reserves today, even factoring in the decades of oil use.